I am planning on buying a bike for my daughter who is 12 yrs. She is growing fast, so I don't want to spend a lot on a bike where she will outgrow it quickly. She is already 5'3".
I am new to bikes, but want to get my family started using bikes. Until now, we've been buying department store bikes for the kids.

I'm considering getting used bike for my daughter, but I'm worried about maintenance. What should I look out for in a used bike? I browsed on CL and narrowed down to a couple of bikes. Are these bikes good for the price?

The bike looks good from the pics but you do have to evaluate it both for size and mechanical soundness. Still the bike looks clean and that is usually a sign that the major parts are OK and/or readily fixable. Also one great thing about buying from CL is that you are recycling a bike that you can sell once your daughter grows out of it and recoup most of your costs.

A hybrid is a fine choice for the kind of riding you intend on doing and these bikes tend not to be too expensive.